CAL. ELEC CODE § 18371 : California Code - Section 18371

(a) No candidate or representative of a candidate, and no proponent, opponent, or representative of a proponent or opponent, of an initiative, referendum, or recall measure, or of a charter amendment, shall solicit the vote of a vote by mail voter, or do any electioneering, while in the residence or in the immediate presence of the voter, and during the time he or she knows the vote by mail voter is voting.

(b) Any person who knowingly violates this section is guilty of a misdemeanor.

(c) This section shall not be construed to conflict with any provision of the federal Voting Rights Act of 1965, as amended, nor to preclude electioneering by mail or telephone or in public places, except as prohibited by Section 18370, or by any other provision of law.